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模仿String.indexOf,判断一个字符串是否包含另一个字符串

程序员文章站 2022-03-08 22:49:34
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目录:
一.方法介绍
二.图示意
三.源代码

一.方法介绍

判断一个字符串str1是否包含另一个字符串str2:
1.取str2的第一个字符一次和str1的字符依次比较,知道找到相等的字符为止或者找完整个str1的length.
2.当找到相等的字符后,在str2长度内str2与str1依次进行比较

二.图示意

[img]http://dl.iteye.com/upload/picture/pic/88520/33d79726-7613-35d1-adea-1b5a069a5790.jpg[/img]

三.源代码

JDK中java.lang.String.indexOf(char[], int, int, char[], int, int, int)源码:

/**
* Code shared by String and StringBuffer to do searches. The
* source is the character array being searched, and the target
* is the string being searched for.
*
* @param source the characters being searched.
* @param sourceOffset offset of the source string.
* @param sourceCount count of the source string.
* @param target the characters being searched for.
* @param targetOffset offset of the target string.
* @param targetCount count of the target string.
* @param fromIndex the index to begin searching from.
*/
static int indexOf(char[] source, int sourceOffset, int sourceCount,
char[] target, int targetOffset, int targetCount,
int fromIndex) {
if (fromIndex >= sourceCount) {
return (targetCount == 0 ? sourceCount : -1);
}
if (fromIndex < 0) {
fromIndex = 0;
}
if (targetCount == 0) {
return fromIndex;
}

char first = target[targetOffset];
int max = sourceOffset + (sourceCount - targetCount);

for (int i = sourceOffset + fromIndex; i <= max; i++) {
/* Look for first character. */
if (source[i] != first) {
while (++i <= max && source[i] != first);
}

/* Found first character, now look at the rest of v2 */
if (i <= max) {
int j = i + 1;
int end = j + targetCount - 1;
for (int k = targetOffset + 1; j < end && source[j] ==
target[k]; j++, k++);

if (j == end) {
/* Found whole string. */
return i - sourceOffset;
}
}
}
return -1;
}



模仿的判断一个字符串是否包含另一个字符串的源码:

public static String compareDoubleString(String source, String target) {
// 分别获取两个字符串的长度,因为后面会用到
int sourceLength = source.length();
int targetLength = target.length();

// 获取目标的第一个字符
char firstTargetChar = target.charAt(0);

// 最多比较的次数
int max = sourceLength - targetLength;
// 如果第一个不相等,那么一直找到相等的那一个或者找完都不能找到
int sourceOffset = -1;
while (++sourceOffset < max
&& source.charAt(sourceOffset) != firstTargetChar) {
}
if (sourceOffset <= max) {
// 设置新的源索引
int newSourceOffset = sourceOffset + 1;
// 剩余的比较长度,也就是在offset上增加targetLength
int leaveLength = newSourceOffset + targetLength - 1;
int targetOffset = 1;
// 连续的比较,条件不符合的时候跳出
for (; newSourceOffset < leaveLength
&& source.charAt(newSourceOffset) == target
.charAt(targetOffset); newSourceOffset++, targetOffset++)
;
if (newSourceOffset == leaveLength) {
return "包含:source包含target字符串!";
}
}
return "不包含:source不包含target字符串!";
}



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